Editing ZX Spectrum (section)

=== Development ===
[[File:ZX Spectrum concept.jpg|thumb|An original concept sketch of the ZX Spectrum, depicting an angular and wedge-like form similar to its predecessor, the [[ZX81]] ]]

Development of the ZX Spectrum began in September 1981, a few months after the release of the ZX81. Sinclair resolved to make his own products obsolete before his rivals developed the products that would do so. Parts of designs from the ZX80 and ZX81 were reused to ensure a speedy and cost-effective manufacturing process. The team consisted of 20 engineers housed in a small office at 6 [[King's Parade]], Cambridge.<ref name="edgehistory">{{cite magazine |last1=Brown |first1=Nathan |title=The making of the ZX Spectrum |url=http://www.edge-online.com/features/making-zx-spectrum/ |magazine=[[Edge (magazine)|Edge]] |publisher=[[Future plc]] |access-date=4 April 2021 |archive-url=https://web.archive.org/web/20120425035159/http://www.edge-online.com/features/making-zx-spectrum/ |archive-date=25 April 2012 |location=[[Bath, Somerset|Bath]] |date=23 April 2012}}</ref> During early production, the machine was known as the ZX81 Colour or the ZX82 to highlight the machine's colour display, which differed from the black and white of its predecessors. The addendum "Spectrum" was added later on, to emphasise its 15-colour palette.{{sfn|Leigh|2018|p=68}} Aside from a new [[crystal oscillator]] and extra chips to add additional [[kilobyte]]s of memory,{{sfn|Adams|1982|p=14}} the ZX Spectrum was intended to be, as quoted by Sinclair's marketing manager, essentially a "ZX81 with colour".<ref name=edgehistory/> According to Sinclair, the team also wanted to combine the ZX81's separate [[random-access memory]] sections for audio and video into a single bank.<ref name="registerlegacy">{{cite web |last1=Speed |first1=Richard |title=Sinclair's 8-bit home computer, ZX Spectrum, turns 40 |url=https://www.theregister.com/2022/04/22/spectrum_at_40/ |website=The Register |publisher=Situation Publishing |access-date=2 October 2023 |archive-url=https://web.archive.org/web/20230526232039/https://www.theregister.com/2022/04/22/spectrum_at_40/ |archive-date=26 May 2023 |location=London |language=en |date=22 April 2022}}</ref>

Chief engineer [[Richard Altwasser]] was responsible for the ZX Spectrum's hardware design. His main contribution was the design of the semi-custom [[Gate array|uncommitted logic array]] (ULA) integrated circuit, which integrated, on a single chip, the essential hardware functions. Altwasser designed a graphics mode that required less than 7 kilobytes of memory and implemented it on the ULA. Vickers wrote most of the ROM code. Lengthy discussions between Altwasser and Sinclair engineers resulted in a broad agreement that the ZX Spectrum must have high-resolution graphics, 16 kilobytes of memory, an improved [[Cassette tape#data|cassette interface]], and an impressive colour palette.{{sfn|Gore|1982|p=38}} To achieve this, the team had to divorce the [[central processing unit]] (CPU) away from the main display to enable it to work at full efficiency – a method which contrasted with the ZX81's integrated CPU.{{sfn|Gore|1982|p=38}} The inclusion of colour to the display proved a major obstacle to the engineers. A [[Teletext]]-like approach was briefly considered, in which each line of text would have colour-change codes inserted into it. However, this was ruled out, as it was deemed unsuitable for high-resolution graphs or diagrams that involved multiple colour changes. Altwasser devised the idea of allocating a [[BIOS color attributes|colour attribute]] to each character position on the screen. This ultimately used eight [[bit]]s of memory for each character position; three bits to provide any one of eight foreground colours and three bits for the eight [[Web colors|background colours]], one bit for extra brightness and one bit for flashing. Overall, the system took up slightly less than 7 kilobytes of memory, leaving an additional 9 kilobytes to write programs&nbsp;– a figure that pleased the team.{{sfn|Gore|1982|pp=38-39}}

Much of the firmware was written by computer scientist [[Steve Vickers (computer scientist)|Steve Vickers]] from Nine Tiles,<ref name="registerlegacy"/> who compiled all control routines to produce the [[Sinclair BASIC]] interpreter, a custom variant of the general purpose [[BASIC]] programming language. Making a custom interpreter made it possible to fit all of its functionality into a very small amount of [[read-only memory]] (ROM).{{sfn|Adams|1982|p=14}} The development process of the software was marked by disagreements between Nine Tiles and Sinclair Research. Sinclair placed an emphasis on expediting the release of the Spectrum, primarily by minimising alterations in the software from the ZX81, which had in turn been based on the ZX80's software. The software architecture of the ZX80, however, had been tailored for a severely constrained memory system, and in Nine Tiles' opinion was unsuitable for the enhanced processing demands of the ZX Spectrum. Sinclair favoured solving this with expansion modules on the existing framework like with the ZX81, which Nine Tiles disagreed with. Ultimately, both designs were developed, but Vickers and Nine Tiles were unable to finish their version before the launch of the Spectrum and it was not used.{{sfn|Adamson|Kennedy|1986|pp=84-88}}

[[File:Rick Dickinson.jpg|thumb|left|Designer [[Rick Dickinson]] in the [[Sinclair Research]] Cambridge office in 1983]]
The distinctive case and colourful design of the ZX Spectrum was the creation of [[Rick Dickinson]], a young British industrial designer who had been hired by Sinclair to design the ZX81. Dickinson was tasked to design a sleeker and more "marketable" appearance to the new machine, whilst ensuring all 192 BASIC functions could fit onto 40 physical keys.<ref name=edgehistory/> Early sketches from August 1981 showed the case was to be more angular and wedge-like, in similar vein to an upgraded ZX81 model. Dickinson later settled on a flatter design with a raised rear section and rounded sides in order to depict the machine as "more advanced" as opposed to a mere upgrade. In drawing up potential logos, Dickinson proposed a series of different logotypes which all featured rainbow slashes across the keyboard.<ref name=registerhistory/>

The design of the Spectrum's [[Chiclet keyboard|rubber keyboard]] was simplified from several hundred components to a conventional moving keyboard down to "four to five" moving parts using a new technology.<ref name="bbc30">{{cite web |last1=Kelion |first1=Leo |title=ZX Spectrum's chief designers reunited 30 years on |url=https://www.bbc.co.uk/news/technology-17776666 |website=[[BBC News]] |publisher=[[BBC]] |access-date=2 October 2023 |archive-url=https://web.archive.org/web/20230418150809/https://www.bbc.co.uk/news/technology-17776666 |archive-date=18 April 2023 |location=London |date=19 April 2012}}</ref> The keyboard was still undergoing changes as late as February 1982; some sketches included a roundel-on-square key design which was later featured on the later Spectrum+ model.<ref name=registerhistory/> Dickinson recalled in 2007 that "everything was cost driven" and that the minimalist, [[Bauhaus]] approach to the Spectrum gave it an elegant yet "[non] revolutionary" form.<ref name=bbclegacy/> The drawing board on which Dickinson designed the ZX Spectrum is now on display in the [[Science Museum, London|Science Museum]] in London.<ref>{{cite web |title=Sinclair Spectrum designer Rick Dickinson dies in US |url=https://www.bbc.co.uk/news/technology-43907248 |website=[[BBC News]] |publisher=[[BBC]] |archive-url=https://web.archive.org/web/20230930220700/https://www.bbc.co.uk/news/technology-43907248 |archive-date=30 September 2023 |location=London |date=26 April 2018}}</ref><ref>{{cite web |title=Alpia drawing board - Science Museum Group Collection |url=https://collection.sciencemuseumgroup.org.uk/objects/co8087251/alpia-drawing-board-used-by-rick-dickinson-to-des-drawing-board |publisher=The Science Museum Group |access-date=9 October 2023 |archive-url=https://web.archive.org/web/20221129031620/https://collection.sciencemuseumgroup.org.uk/objects/co8087251/alpia-drawing-board-used-by-rick-dickinson-to-des-drawing-board |archive-date=29 November 2022 |location=London |language=en}}</ref>

The need for an improved cassette interface was apparent from the number of complaints received from ZX81 users, who encountered problems when trying to save and load programs.{{sfn|Gore|1982|p=39}} To increase the data transfer speed, the team significantly decreased the length of tones that represent binary data.{{sfn|Gore|1982|p=39}} To increase the reliability, a leading period of [[pure tone|constant tone]] was introduced, which allowed the cassette recorder's [[automatic gain control]] to settle itself down, eliminating hisses on the tape.{{sfn|Gore|1982|p=39}} A [[Schmitt trigger]] was added inside the ULA to reduce noise of the received signal.{{sfn|Gore|1982|p=39}} Originally, the team aimed for data transfer speed of 1000 [[baud]], but succeeded in getting it to work at a considerably faster 1500 baud.{{sfn|Gore|1982|p=39}} Unlike the ZX81, the Spectrum was able to maintain its display during loading and saving operations, and programmers took advantage of this to show a [[splash screen]] whilst loading took place in the background.

As with the ZX81, the ZX Spectrum was manufactured in [[Dundee]], Scotland, by [[Timex Group USA|Timex Corporation]] at the company's [[Dryburgh, Dundee district|Dryburgh]] factory.<ref name="Day">{{cite news|last1=Day|first1=Peter|title=How Dundee became a computer games centre|work=[[BBC News]]|location=London|date=9 September 2014|url=https://www.bbc.co.uk/news/business-29122873|access-date=12 November 2016|url-status=live|archive-url=https://web.archive.org/web/20161009014928/http://www.bbc.co.uk/news/business-29122873|archive-date=9 October 2016}}</ref><ref>{{cite web |title=ZX Spectrum Computer and associated game cassettes |url=https://www.themcmanus-dundee.gov.uk/content/collections/database/zx-spectrum-computer-and-associated-game-cassettes |website=The McManus |publisher=Dundee Art Gallery |access-date=3 October 2023 |archive-url=https://web.archive.org/web/20231003134524/https://www.themcmanus-dundee.gov.uk/content/collections/database/zx-spectrum-computer-and-associated-game-cassettes |archive-date=3 October 2023 |location=[[Dundee]] |language=English |date=20 January 2012}}</ref> Prior to the manufacture of the ZX81, however, Timex had little experience in assembling electronics and had not originally been an obvious choice of manufacturing subcontractor. It was a well-established manufacturer of mechanical watches but was facing a crisis at the beginning of the 1980s; profits had dwindled to virtually zero as the market for watches stagnated in the face of competition from the [[Watch#Digital|digital]] and [[Quartz clock|quartz watches]]. Recognising the trend, Timex's director, [[Fredrik Olsen|Fred Olsen]], determined that the company would diversify into other areas and signed a contract with Sinclair.{{sfn|Adamson|Kennedy|1986|p=94}}